Video encoding apparatus, video decoding apparatus, and video decoding method for performing intra-prediction based on directionality of neighboring block

1. A video decoding method performed by a video decoding apparatus, the method comprising:

reconstructing a residual block of a current block from an input bitstream;

selecting an intra mode for the current block from among a plurality of intra modes, wherein the number of the plurality of intra modes for a 32×32 block is equal to the number of intra modes for a 16×16 block, and the number of the plurality of intra modes for the 32×32 block is equal to the number of intra modes for an 8×8 block;

performing intra-prediction according to the selected intra mode for the current block to generate a prediction block for the current block; and

adding the residual block of the current block to the prediction block for the current block to reconstruct the current block,

wherein the number of the plurality of intra modes is greater than 9 corresponding to the number of a plurality of intra modes specified in the H.264 standard,

wherein the plurality of intra modes includes a plurality of directional modes, each of the plurality of directional modes has a direction, the direction has a slope defined as dy in a vertical direction over dx in a horizontal direction, and dx and dy are integer numbers,

wherein selecting the intra mode for the current block comprises:

determining an intra mode for a neighboring block; and

selecting the intra mode for the current block based on whether the determined intra mode for the neighboring block is a directional mode or a non-directional mode,

wherein the intra mode for the current block is selected by using a first set of one or more mathematical expressions, if the determined intra mode for the neighboring block is the directional mode,

wherein the intra mode for the current block is selected by using a second set of one or more mathematical expressions, if the determined intra mode for the neighboring block is the non-directional mode, and

wherein the second set of one or more mathematical expressions is different from the first set of one or more mathematical expressions.

2. The video decoding method of claim 1 , wherein the number of the plurality of directional modes is greater than 8 corresponding to the number of a plurality of directional modes specified in the H.264 standard.

3. The video decoding method of claim 2 , wherein the number of the plurality of intra modes is fixed as a same value regardless of a block size of the current block.

4. The video decoding method of claim 3 , wherein all of the 8×8 block, the 16×16 block, and the 32×32 block are allowed for the intra-prediction using the plurality of intra modes, and

wherein the number of the plurality of intra modes is fixed as the same value regardless of the block size of the current block when the current block is the 8×8 block, the 16×16 block, or the 32×32 block.

5. The video decoding method of claim 4 , wherein the number of intra modes for the 16×16 block is not smaller than the number of a plurality of intra modes for a 4×4 block.

6. The video decoding method of claim 1 , wherein performing the intra-prediction comprises:

obtaining the prediction block of the current block from at least one neighboring block of the current block according to the directionality of the selected intra mode.

7. The video decoding method of claim 6 , wherein the at least one neighboring block includes at least one of an upper block, a left block, an upper left block, and an upper right block with respect to the current block.

8. The video decoding method of claim 1 , further comprising:

performing inter-prediction to generate a prediction block of the current block by performing motion compensation when the current block has been coded using inter-prediction,

wherein the current block to be decoded using inter-prediction is obtained by dividing an input image block asymmetrically.

9. The video decoding method of claim 1 , wherein the number of intra modes for the 8×8 block is greater than 9 corresponding to the number of the plurality of intra modes specified in the H.264 standard when the current block is the 8×8 block.

10. The video decoding method of claim 1 , wherein when the current block is the 16×16 block, the number of intra modes for the 16×16 block is greater than 9 corresponding to the number of the plurality of intra modes specified in the H.264 standard when the current block is the 16×16 block.

11. The video decoding method of claim 1 ,

wherein selecting the intra mode for the current block based on whether the determined intra mode for the neighboring block is the directional mode or the non-directional mode comprises:

determining candidate intra modes based on whether the determined intra mode for the neighboring block is the directional mode or the non-directional mode; and

selecting the intra mode for the current block from among the candidate intra modes,

wherein the candidate intra modes are determined by using the first set of one or more mathematical expressions, if the determined intra mode for the neighboring block is the directional mode, and

wherein the candidate intra modes are determined by using the second set of one or more mathematical expressions, if the determined intra mode for the neighboring block is the non-directional mode.

12. The video decoding method of claim 11 , wherein selecting the intra mode for the current block from among the candidate intra modes comprises:

obtaining information for selecting the intra mode for the current block from among the candidate intra modes; and

selecting the intra mode for the current block from among the candidate intra modes based on the obtained information.

13. The video decoding method of claim 1 , wherein the non-directional mode includes a direct current (DC) mode.